A transmission is any mechanical linkage that converts an input torque to an output torque. It usually involves a series of gears that have differing diameters, allowing a first gear at a first rotation rate to link to a second gear rotating at a second rate. The most common application for transmissions is in a vehicle. For example, a car may have an automatic transmission or a manual transmission. A bicycle has a transmission that links the pedals to the hub of the rear wheel.
Transmissions allow an input force to be converted into a more useful and appropriate output. However, by using gears and linkages, a typical transmission may only have 4 or 5 ratios available. For example, a four speed automatic transmission in a car has only 4 sets of output gears to couple to the engine's input. A ten speed bike has only ten ratios of input to output. A need exists for a transmission that is not limited by the number of gears. Yet, to place a larger number of gears into a transmission increases its costs and weight and space requirements.
A continuously variable transmission (CVT) is a transmission that eliminates the need for a specified number of gears. Instead it allows an almost limitless number of input to output ratios. This is a benefit because it allows an output to be achieved, i.e. the speed of a vehicle, at an optimal input, i.e. the rpm of the engine. For example, an engine might be most efficient at 1800 rpm. In other words, the peak torque output for the engine might be achieved at this engine rpm, or perhaps the highest fuel economy. Yet, in third gear, the car might be going faster at 1800 rpm than the driver desires. A continuously variable transmission would allow an intermediate ratio to be achieved that allowed the optimal input to achieve the desired output.
There are several examples of continuously variable transmissions. U.S. Pat. No. 6,419,608 is entitled “Continuously Variable Transmission” and is owned by Fallbrook Technologies of San Diego, Calif. It discloses a CVT that uses a series of rolling spheres, also called power adjusters, to couple the input and output. Referring to FIGS. 1 and 2, a prior art continuously variable transmission 100 is disclosed such as the one in the Fallbrook Technologies '608 patent. The transmission 100 is shrouded in a hub shell 40 covered by a hub cap 67. At the heart of the transmission 100 are three or more power adjusters 1a, 1b, 1c which are spherical in shape and are circumferentially spaced equally around the centerline or axis of rotation of the transmission 100. As seen more clearly in FIG. 2, spindles 3a, 3b, 3c are inserted through the center of the power adjusters 1a, 1b, 1c to define an axis of rotation for the power adjusters 1a, 1b, 1c. In FIG. 1, the power adjuster's axis of rotation is shown in the horizontal direction. Spindle supports 2a-f are attached perpendicular to and at the exposed ends of the spindles 3a, 3b, 3c. In one embodiment, each of the spindles supports has a bore to receive one end of one of the spindles 3a, 3b, 3c. The spindles 3a, 3b, 3c also have spindle rollers 4a-f coaxially and slidingly positioned over the exposed ends of the spindles 3a, 3b, 3c outside of the spindle supports 2a-f. 
As the rotational axis of the power adjusters 1a, 1b, 1c is changed by tilting the spindles 3a, 3b, 3c, each spindle roller 4a-f follows in a groove 6a-f cut into a stationary support 5a, 5b. Referring to FIGS. 1 and 3, the stationary supports 5a, 5b are generally in the form of parallel disks with an axis of rotation along the centerline of the transmission 100. The grooves 6a-f extend from the outer circumference of the stationary supports 5a, 5b towards the centerline of the transmission 100. While the sides of the grooves 6a-f are substantially parallel, the bottom surface of the grooves 6a-f forms a decreasing radius as it runs towards the centerline of the transmission 100. As the transmission 100 is shifted to a lower or higher gear by changing the rotational axes of the power adjusters 1a, 1b, 1c, each pair of spindle rollers 4a-f located on a single spindle 3a, 3b, 3c, moves in opposite directions along their corresponding grooves 6a-f. 
Referring to FIGS. 1 and 3, a centerline hole 7a, 7b in the stationary supports 5a, 5b allows the insertion of a hollow shaft 10 through both stationary supports 5a, 5b. Referring to FIG. 4, in an embodiment of the invention, one or more of the stationary support holes 7a, 7b may have a non-cylindrical shape 14, which fits over a corresponding non-cylindrical shape 15 along the hollow shaft 10 to prevent any relative rotation between the stationary supports 5a, 5b and the hollow shaft 10. If the rigidity of the stationary supports 5a, 5b is insufficient, additional structure may be used to minimize any relative rotational movement or flexing of the stationary supports 5a, 5b. This type of movement by the stationary supports 5a, 5b may cause binding of the spindle rollers 4a-f as they move along the grooves 6a-f. 
Referring back to FIGS. 1 and 3, the stationary support 5a is fixedly attached to a stationary support sleeve 42, which coaxially encloses the hollow shaft 10 and extends through the wall of the hub shell 40. The end of the stationary support sleeve 42 that extends through the hub shell 40 attaches to the frame support and preferentially has a non-cylindrical shape to enhance subsequent attachment of a torque lever 43. As shown more clearly in FIG. 7, the torque lever 43 is placed over the non-cylindrical shaped end of the stationary support sleeve 42, and is held in place by a torque nut 44. The torque lever 43 at its other end is rigidly attached to a strong, non-moving part, such as a frame (not shown). A stationary support bearing 48 supports the hub shell 40 and permits the hub shell 40 to rotate relative to the stationary support sleeve 42.
Referring back to FIGS. 1 and 2, shifting is manually activated by axially sliding a rod 11 positioned in the hollow shaft 10. One or more pins 12 are inserted through one or more transverse holes in the rod 11 and further extend through one or more longitudinal slots 16 (not shown) in the hollow shaft 10. The slots 16 in the hollow shaft 10 allow for axial movement of the pin 12 and rod 11 assembly in the hollow shaft 10. As the rod 11 slides axially in the hollow shaft 10, the ends of the transverse pins 12 extend into and couple with a coaxial sleeve 19. The sleeve 19 is fixedly attached at each end to a substantially planar platform 13a, 13b forming a trough around the circumference of the sleeve 19.
As seen more clearly in FIG. 4, the planar platforms 13a, 13b each contact and push multiple wheels 21a-f. The wheels 21a-f fit into slots in the spindle supports 2a-f and are held in place by wheel axles 22a-f. The wheel axles 22a-f are supported at their ends by the spindle supports 2a-f and allow rotational movement of the wheels 21a-f. 
Referring back to FIGS. 1 and 2, the substantially planar platforms 13a, 13b transition into a convex surface at their outer perimeter (farthest from the hollow shaft 10). This region allows slack to be taken up when the spindle supports 2a-f and power adjusters 1a, 1b, 1c are tilted as the transmission 100 is shifted. A cylindrical support member 18 is located in the trough formed between the planar platforms 13a, 13b and sleeve 19 and thus moves in concert with the planar platforms 13a, 13b and sleeve 19. The support member 18 rides on contact bearings 17a, 17b located at the intersection of the planar platforms 13a, 13b and sleeve 19 to allow the support member 18 to freely rotate about the axis of the transmission 100. Thus, the bearings 17a, 17b, support member 18, and sleeve 19 all slide axially with the planar platforms 13a, 13b when the transmission 100 is shifted.
Now referring to FIGS. 3 and 4, stationary support rollers 30a-l are attached in pairs to each spindle leg 2a-f through a roller pin 31a-f and held in place by roller clips 32a-l. The roller pins 31a-f allow the stationary support rollers 30a-l to rotate freely about the roller pins 31a-f The stationary support rollers 30a-l roll on a concave radius in the stationary support 5a, 5b along a substantially parallel path with the grooves 6a-f As the spindle rollers 4a-f move back and forth inside the grooves 6a-f, the stationary support rollers 30a-l do not allow the ends of the spindles 3a, 3b, 3c nor the spindle rollers 4a-f to contact the bottom surface of the grooves 6a-f to maintain the position of the spindles 3a, 3b, 3c, and to minimize any frictional losses.
While a continuously variable transmission is artful on paper, the realities of making one work smoothly requires significant effort. For example, a need exists for a method to axially shift the rod 11. Such a shifter would be useful in any environment that the CVT is used. It is also important to consider the difficulties of reducing a CVT in size to work on a bicycle. A need also exists for a method of hand shifting the CVT by the rider.